transformDayElement params to value no date is null how to get date

[zhangwei900808]

when I set value below

<CalendarHeatmap
  startDate={new Date('2021-01-01')}
  endDate={new Date('2021-04-01')}
  values={[
    { date: '2021-01-01', count: 12 },
    { date: '2021-01-22', count: 122 },
    { date: '2021-01-30', count: 38 },
    // ...and so on
  ]}
transformDayElement={(rect, value, index) => {
          console.log('rect=', rect, ',value=', value, ',index=', index)
          const tooltip = (
            <Tooltip mouseEnterDelay={0.001} mouseLeaveDelay={0.001} arrowPointAtCenter placement="top"
                     title={`${value && value.date ? value.date.slice(0, 10) : ''} 数量: ${value && value.count}`}
                     key={index}>{rect}</Tooltip>
          );
          return tooltip
        }}
/>

but tooltip is show value is null how to get the date